/Engine/Source/Runtime/Slate/Public/Framework/Docking/LayoutExtender.h
Extend the layout by defining a tab before or after the specified predicate tab ID
void ExtendLayout ( [FTabId](API\Runtime\Slate\Framework\Docking\FTabId) PredicateTabId, ELayoutExtensionPosition Position, [FTabManager::FTab](API\Runtime\Slate\Framework\Docking\FTabManager\FTab) TabToAdd )